Video doesn't autoplay (phone, tablet)
Mobile devices and tablets have a limitation, that you can't autoplay videos on them, because of the common usage of mobile internet, and the memory available on them, so only a user's action can start a video. This option is defined by the mobile browsers, and we can't really do anything about this.
If you are using background video, that won't appear at all in mobile devices because of this, so you should rather select a background image as a fallback for your mobile / tablet users.
The latest browsers and devices started to support autoplaying videos on them, if your video is muted.